1. Field of the Invention
The present invention relates to a single-crystal diamond growth base material and a method for manufacturing a single-crystal diamond substrate.
2. Description of the Related Art
Diamond has a wide band gap of 5.47 eV and also has a very high dielectric breakdown electric field intensity of 10 MV/cm. Further, since it has thermal conductivity that is the highest value among materials, using the diamond is advantageous for a high-output power device.
Furthermore, the diamond has high drift mobility and, even if its Johnson performance index is compared, the diamond is most advantageous as a high-speed power device among semiconductors.
Therefore, it is said that the diamond is an ultimate semiconductor suitable for a high-frequency/high-output electronic device. Accordingly, studies on various kinds of electronic devices utilizing single-crystal diamond as a substrate have been advanced.
At present, in many cases, the single-crystal diamond for fabrication of a diamond semiconductor is diamond called an Ib type synthesized by a high-temperature and high-pressure method (HPHT) or an IIa type having improved purity.
However, the HPHT single-crystal diamond having high crystallinity can be obtained but, on the other hand, increasing its size is difficult, and a price extremely rises as the size increases, whereby practical realization as a device substrate is difficult.
Thus, to provide an inexpensive single-crystal diamond substrate having a large area, CVD single-crystal diamond synthesized by a vapor phase method has been also studied.
In recent years, as single-crystal diamond, homoepitaxial CVD single-crystal diamond homoepitaxially grown directly on an HPHT single-crystal diamond base material (a seed base material) by a vapor-phase synthesis method has been also reported (see the 20th diamond symposium lecture summary (2006), pp. 6-7.).
According to this method, since the base material and the grown single-crystal diamond are formed of the same material, they are hardly separated from each other, and hence there are problems in cost, e.g., requiring ion implantation into the base material in advance or requiring a prolonged wet etching separation treatment even after the growth. Further, the crystallinity of the obtained single-crystal diamond is lowered to some extent since ions are implanted into the base material.
As another method, CVD single-crystal diamond heteroepitaxially grown by a CVD method on an single-crystal iridium (Ir) film heteroepitaxially grown on a single-crystal MgO base material (a seed base material) has been also reported (see Jpn. J. Appl. Phys. Vol. 35 (1996) pp. L1072-L1074).
However, this method has a problem that the base material and the grown single-crystal diamond are broken into pieces due to stress (a sum of internal stress and thermal stress) generated between the single-crystal MgO substrate and the single-crystal diamond grown via the single-crystal Ir film.